This type of drainage mat is old in the art (cf. West German Laid-open Application Nos. 2,248,911, 2,263,846, 2,327,618, 2,551,267). In these drainage mats of known construction, the grains are arranged in multilayers and are in contact with one another. This type of packing results in a small water-removal capacity for these known drainage mats, so that they become thick if the water-removal capacity is to be increased, resulting in a large increase in the weight per square meter of such drainage mats. The grains can be secured only by the two fabrics, resulting in mutual displacement of the grains and thereby in frictional stress on the fabrics during compression loading. Frequently, the fabrics cannot be prevented from tearing open. In other cases, the grains are held in place by stitching-through fibers from the two fabrics or by spraying binders. Such drainage mats are very expensive to make. The free space for the water removal is further reduced by the stitched-through fibers or by the binder. In such drainage mats, one of the fabrics is basically a filter layer, e.g. a filament layer or nonwoven fabric, while the other fabric can be a filter layer or a tightly woven sheet, e.g. a film.